MANUFACTURE OF ELONGATE ARTICLES

Abstract: A method of manufacturing an elongate article such as a golf club shaft. The method comprising forming an elongate hollow polymer core 10 by gas injection moulding. A plurality of layers (12, 14, 16, 18, 20, 22) of a curable material are wrapped around the core. The layers have uniaxial reinforcement with the reinforcement in respective layers inclined relative to each other. The wrapped core is subsequently cured.

Description: Manufacture of Elongate Articles This invention concerns a method of manufacturing elongate articles and articles made by this method, and particularly but not exclusively a method of manufacturing golf club shafts and shafts manufactured by this method. With golf club shafts there are a number of important different characteris ics. These include flex, torque, strength and weight. Originally wooden golf club shafts were used but subsequently steel shafts became the norm. More recently shafts have also been made from composite materials. Such composite shafts have conventionally been made by wrapping a plurality of layers of reinforced resinous material, usually between ten and fifteen layers, around a steel andrel. The arrangement formed is subsequentl cured and the mandrel removed after curing. Considerable force may be required to remove the mandrel. Forming shafts in this way involves a large number of production steps and can also result in somewhat expensive and relatively heavy shafts . According to the present invention there is provided a method of manufacturing an elongate article, the method comprising forming an elongate hollow polymer core by injection moulding, wrapping a plurality of layers of a curable reinforced material around the core, and curing the subsequently formed wrapped core. The core is preferably formed by gas injection moulding. The core is preferably formed in a closed mould, and measured amounts of gas and polymer are desirably introduced into the mould. The gas is preferably introduced into the mould simultaneously with the polymer after a first portion of polymer has already been introduced thereinto. The polymer preferably includes reinforcing fibres which may be carbon fibre or boron. The polymer is preferably nylon based. The curable material is preferably epo y based and desirably has carbon fibre reinforcement. The reinforcement of the curable material is preferably substantially uniaxial. One or more of the layers of curable material is preferably arranged such that the reinforcement therein lies substantially parallel to the longitudinal direction of the article. Another of the layers is preferably arranged such that the reinforcement is inclined relative to the longitudinal direction of the article. Said inclination is preferably between 25 and 45° and may be substantially 30°. A still further layer is preferably inclined at a similar angle but in an opposite direction . The layers of curable material preferably comprise strips of material aligned parallel to the longitudinal direction of the article. The strips of material are preferably of a size to substantially completely surround the core with no overlap. Alternatively, the curable material may be wrapped around the core a plurality of times along the length thereof. Preferably after the curable material is wrapped around the core and before curing, shrink wrap tape is applied around the curable material to cause consolidation during curing. After curing the article is preferably ground which may remove the shrink wrap tape. The temperature of curing of the wrapped core is preferably such that during curing the core becomes tacky and fuses with the wrapped material. Also according to the present invention there is provided an elongate article manufactured by a method according to any of the proceeding ten paragraphs. The invention further provides a golf club shaft manufactured by a method according to any of said preceding ten paragraphs. Extra layers of curable material may be provided at particular places along the length of the shaft. For instance, an extra layer or layers may be provided at the head end of the shaft. The shaft preferably tapers outwardly away from the head end. The shaft may have parallel sides in the region adjacent the head end. Alternatively, the invention may provide an elongate article in the form of an aerial or fishing rod according to any of said ten proceeding paragraphs. The article may comprise a plurality of connectable sections, with connecting means on the ends of the respective sections. The connection means may be formed on the core during moulding. An embodiment of the present invention will now be described by way of example only with reference to the single figure of the accompanying drawings which shows a diagrammatic part cut-away perspective view of a golf club shaft according to the invention. This shaft was made by the following method. A hollow core 10 was formed by gas injection moulding. The core 10 was formed in a closed mould by first introducing a small portion of polymer into the mould then simultaneously introducing further polymer and nitrogen gas and maintaining the gas under pressure until the polymer had solidified. The polymer comprises 30?ό reinforced impact modified carbon fibre nylon (nylon 66). The core has parallel sides for the first 225mm from the head end and subsequently tapers outwardly. The parallel sided end ensures that the head end of the shaft is of a correct size to fit into a club head even if the shaft is shortened to suit a particular player. Following moulding the core 10 is subject to centreleεs grinding to remove flashing and any handling contamination . A layer 12 of high modulus epoxy based carbon fibre prepreg (HM55 - Torayca) is wrapped on the core 10. The fibres in the prepreg of the layer 12 are unidirectional and are aligned parallel to the longitudinal direction of the core 10. The layer 12 is formed from an elongate strip of a size to fully surround the core 10 but not overlap. A further layer 14 of a similar prepreg is wrapped around the layer 12 but with the fibres inclined at 30° relative to the axial direction of the core 10. A further similar layer 16 is wrapped around the layer 14 with the fibres inclined at 30° to the axial direction but in an opposite direction. A layer 18 of a standard modulus prepreg (T300 Torayca) is wrapped around the layer 16 with the fibres aligned parallel to the axial direction of the core 10. The straight sided portion of the core 10 is strengthened with a boron filament prepreg (not shown) ith the fibres therein aligned parallel to the axial direction of the core 10. A further high modulus prepreg layer 20 is provided again with the fibres aligned parallel to the core 12. A still further layer 22 may be applied of a standard or lightweight modulus prepreg. Following v.'rapping of the prepreg layers 12-22, shrink wrapped tape (not shown) is wrapped around the wrapped core. The rapped core is then cured at 120° for one hour fifty minutes. During this time the prepreg layers 12-22 cure and the tape shrinks consolidating the structure formed. The nylon core 10 also becomes tacky and bonds with the innermost layer 12. Following curing the shaft is subject to centreless grinding to remove the shrink wrapped tape and perhaps some of the outermost layer 22. The shaft is then ready for painting . There is thus provided a golf club shaft with a number of advantageous features. The shaft described would be extra stiff with a 2° torque and thus suitable for use by a professional golfer. Despite having these characteristics the shaft only has 6/7 layers of prepreg and is consequently quite light. Using the method of manufacture according to the present invention involves considerably less labour than conventional methods. Furthermore the use of the injection moulded core considerably reduces the cost of materials used. It is to be understood that the number and characteristics of the layers used can be varied as is required. Moreover, it may be possible to use other injection moulding techniques. In some instances it may be possible to use filament winding rather than rapping as described. Curing conditions are obviously chosen to suit the particular materials used but it is advantageous for bonding to occur between the innermost layer and the core. It is also to be understood that this invention is not to be restricted to golf club shafts. This method of manufacture is also suited to manufacturing other elongate articles such as aerials or fishing rods. Such articles may be made on a number of sections and suitable connection means such as screw threads or a bayonet fitting may be provided in the core during moulding. Obviously many different materials may used other than those described. Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims: C l a i m s : 1. A method of manufacturing an elongate article, the method comprising forming an elongate hollow polymer core (10) by injection moulding, characterised in that the method also comprises wrapping a plurality of layers (12,1 ,16,18,20,22) of a curable reinforced material around the core (10), and curing the subsequently formed wrapped core . 2. A method according to claim 1 , characterised in that the core (10) is formed by gas injection moulding. 3. A method according to claim 2, characterised in that the core (10) is formed in a closed mould. 4. A method according to claims 2 or 3, character sed in that measured amounts of gas and polymer are introduced into the mould. 5. A method according to claim 4, characterised in that the gas is introduced into the mould simultaneously with the polymer after a first portion of polymer has already been introduced thereinto. A method according to any of the preceding claims, charac erised in that the polymer includes reinforcing fibres . 7. A method according to claim 6, characterised in that the reinforcing fibres are carbon fibre. 8. A method according to claim 6, characterised in that the reinforcing fibres are boron. 9. A method according to any of the preceding claims, characterised in that the polymer is nylon based. 10. A method according to any of the preceding claims, characterised in that the curable material is epoxy based . 11. A method according to any of the preceding claims, characterised in that the curable material has carbon fibre reinforcement. 12. A method according to Claim 11, characterised in that the reinforcement of the curable material is substantially uniaxial. 13. A method according to claim 12, characterised in that one or more of the layers (12,18,20,22) of curable material is arranged such that the reinforcement therein lies substantially parallel to the longitudinal direction of the article. 14. A method according to claims 12 or 13, characterised in that one or more of the layers (14,16) is arranged such that the reinforcement is inclined relative to the longitudinal direction of the article. 15. A method according to claim 14, characterised in that said inclination is between 25 and 45°. 16. A method according to claim 15, characterised in that said inclination is substantially 30°. 17. A method according to any of claims 14 to 16, characterised in that a further layer (16) is inclined at a similar angle but in an opposite direction. 18. A method according to any of the preceding claims, characterised in that the layers (12,14,16,18,20,22) of curable material comprise s rips of material aligned parallel to the longitudinal direction of the article. 19. A method according to claim 18, characterised in that the strips of material are of a size to substantially completely surround the core (10) with no overlap . 20. A method according to any of claims 1 to 17, characterised in that the curable material is wrapped around the core (10) a plurality of times along the length thereof. 21. A method according to any of the preceding claims, characterised in that after the curable material is wrapped around the core (10) and before curing, shrink wrap tape is applied around the curable material to cause consolidation during curing. 22. A method according to claim 21 , characterised in that after curing the article is ground which may remove the shrink wrap tape. 23. A method according to any of the preceding claims, characterised in that the temperature of curing of the wrapped core (10) is such that during curing the core (10) becomes tacky and fuses with the wrapped material. 24. An elongate article characterised in that the article is manufactured by a method according to any of claims 1 to 23. 25. A golf club shaft characterised in that the shaft is manufactured by a method according to any of claims 1 to 23. 26. A shaft according to claim 25, characterised in that extra layers of curable material are provided at particular places along the length of the shaft. 27. A shaft according to claim 26, characterised in that an extra layer or layers is provided at the head end of the shaft. 28. A shaft according to any of claims 25 to 27, characterised in that the shaft tapers outwardly away from the head end. 29. A shaft according to any of claims 25 to 28, characterised in that the shaft has parallel sides in the region adjacent the head end. 30. An elongate article in the form of an aerial or fishing rod characterised in that the article is manufactured by a method according to any of claims 1 to 23. 31. An article according to claim 30, characterised in that the article comprises a plurality of connectable sections, with connecting means on the ends of the respective sections. 32. An article according to claim 31 , characterised in that the connection means are formed on the core during moulding.

Inventors: WRIGHT CHARLES WILLIAM, WRIGHT, CHARLES, WILLIAM
Applicants: OAKBRAY INVEST CO LTD, WRIGHT CHARLES WILLIAM, OAKBRAY INVESTMENT COMPANY LIMITED, WRIGHT, CHARLES, WILLIAM
Application year: 1994
Main classification: B29C70
IPC codes: A63B53, B29C53, B29C70, B29K105